Due to the increasing scarcity of fluid fossil fuels such as oil and natural gas, much attention is being directed towards converting solid carbonaceous materials such as coal, oil shale, and solid waste to liquid and gaseous hydrocarbons by pyrolyzing the solid carbonaceous material. Typically, pyrolysis occurs under nonoxidizing conditions in the presence of a particulate source of heat.
In the past, pyrolysis has been carried out in reactors with long pyrolysis times. These reactors provide a yield of middle boiling hydrocarbons, i.e., C.sub.5 hydrocarbons to hydrocarbons having an end point of about 950.degree. F., less than desired. Their loss has been attributed to protracted effective pyrolysis times which result in thermal cracking of such hydrocarbons.
Tubular reactors providing a short pyrolysis time result in increased yield of middle distillates. However, a disadvantage of using tubular reactors for pyrolysis is a caking or agglomeration problem. Experience with agglomerative coals, particularly Eastern United States coals, indicates that these coals pass through a "tacky" stage during which the coal particles have a tendency to agglomerate in a tubular reactor, especially along the walls of the reactor.
A need exists therefore for a more efficient pyrolysis process and a more efficient pyrolysis reactor which maximizes the yield of the middle boiling hydrocarbons which are useful for the production of gasoline, diesel fuel, heating fuel, and the like, and which prevent coal from agglomerating along the walls of the reactor.